Poly(aryl ether) polymer resins comprise ether groups linking together various functional groups and aromatic radicals, such as phenylene, substituted phenylene, biphenylene, naphthylene.
Over the years, there has been developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ether) polymers. Processes for the preparation of poly(aryl ether) polymers may be divided into two general classes by method of reaction employed: the electrophilic aromatic substitution method and the nucleophilic aromatic substitution method.
Some of the earliest work, such as by Bonner, U.S. Pat. No. 3,065,205, involves the electrophilic aromatic substitution (viz. Friedel-Crafts-catalyzed) reaction of aromatic diacylhalides with unsubstituted aromatic compounds, such as diphenyl ether. In accordance with this method, polymerization proceeds with liberation of hydrogen halide by a Friedel-Crafts-catalyzed reaction in which an aromatic ring hydrogen is substituted with a cationic species derived from the corresponding acyl halide by use of a Lewis acid catalyst such as aluminum chloride, boron trifluoride or hydrogen fluoride. As is easily understood, this method, however, has disadvantages from a commercial viewpoint because it needs more than a stoichiometric amount of a highly corrosive Lewis acid. Furthermore, electrophilic aromatic substitution methods do not have sufficient versatility for linking aromatic nuclei and freedom from side reactions to effect synthesis of a wide range of high molecular weight polymers.
The evolution of the class of polymers provided by electrophilic aromatic substitution methods to a much broader range of poly(aryl ether) polymers was achieved by Johnson et al., Journal of Polymer Science, A-1, Vol. 5, 1967, pp. 2415-2427; Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of poly(aryl ether) polymers can be formed by the nucleophilic aromatic substitution (solution condensation polymerization) reaction of an activated aromatic dihalide and an aromatic diol in a substantially anhydrous dipolar aprotic solvent at elevated temperature. Ether bonds are formed via displacement of halogen by phenoxide anions with removal of halogen as alkali metal halide. Polycondensations in accordance with this method are, usually, performed in certain sulfoxide or sulfone solvents and the use of these dipolar aprotic solvents is an important feature of the process. The anhydrous dipolar aprotic solvents dissolve both the reactants and the polymers, and their use to enhance the rates of substitution reactions of this general type is well known. By this method, Johnson et al. created a host of new poly(aryl ether) polymers including broad classes of poly(aryl ether ketone) and poly(aryl ether sulphone) polymers which are acceptable for use under stress at high temperatures, often in excess of 150.degree. C., and display thermoplasticity below their temperature of decomposition, but well above 150.degree. C.
Thus, poly(aryl ether) polymers are well known; they can be synthesized from a variety of starting materials; and they can be made with different melting temperatures and molecular weights. Most interesting of the poly(aryl ether) polymers are crystalline, and at sufficiently high molecular weights, they are tough, i.e., they exhibit high values (&gt;50 foot-pounds per cubic inch) in the tensile impact test (ASTM D-1822). They have potential for a wide variety of uses, and their favorable properties class them with the best of the engineering polymers.
There are many patents disclosing nucleophilic aromatic substitution methods for preparing polyarylene polyethers. For example, U.S. Patent Nos. 4,108,837 and 4,175,175 describe the preparation of polyarylene polyethers, and in particular, polysulfones. Several one-step and two-step processes are described in these patents. In a one-step processe, a double alkali metal salt of a dihydric phenol is reacted with a dihalobenzenoid compound in the presence of sulfone or sulfoxide solvents under substantially anhydrous conditions.
In a two-step process, a dihydric phenol is first converted, in situ, in the presence of a sulfone or sulfoxide solvent to the alkali metal salt by reaction with an alkali metal or alkali metal compound. After removing water, a dihalobenzenoid compound is reacted with the double salt. Further, the alkali metal salt of the dihydric phenol may be added in the solvent to the dihalobenzenoid compound either continuously, incrementally or all at once to achieve the polymerization reaction. Several other variations of the process are described in the patents.
Canadian Patent No. 847,963 describes a process for preparing polyarylene polyethers. The process comprises contacting equimolar amounts of dihydric phenol and a dihalobenzenoid compound and at least one mole of an alkali metal carbonate per mole of dihydric phenol. The dihydric phenol is reacted in situ with the alkali metal carbonate to form the alkali metal salt thereof, and the formed salt reacts with the dihalobenzeoid compound to form the polyarylene polyether in the usual fashion.
U.S. Pat. No. 4,176,222 describes the preparation of aromatic polyethers containing SO.sub.2 and/or CO linkages by a nucleophilic reaction utilizing a mixture of sodium carbonate or bicarbonate and a second alkali metal carbonate or bicarbonate. The alkali metal of the second alkali metal carbonate or bicarbonate has a higher atomic number than that of sodium. The second alkali metal carbonate or bicarbonate is used in amounts such that there are 0.001 to 0.2 gram atoms of the alkali metal of higher atomic number per gram atom of sodium. The process is stated to take place faster when the combination of sodium carbonate or bicarbonate and the second alkali metal carbonate or bicarbonate are used. Also, the products are stated to be of higher molecular weight using such a combination.
The patent describes in Example 17 that when the reaction is carried out using only sodium carbonate, a polymer is obtained having a reduced viscosity of 0.60 deciliter per gram as measured in concentrated sulfuric acid at 25.degree. C. at a concentration of one gram per 100 milliliters. However, it is stated in the patent that when the polymer was compression-molded into a film, the film was brittle and dark grey in color. In Example 18 of the patent, the polymerization was carried out using potassium carbonate instead of sodium carbonate and a high molecular weight polymer was produced (reduced viscosity of 1.55 as measured in concentrated sulfuric acid at 25.degree. C. at a concentration of one gram per 100 milliliters). However, the polymer was stated to contain a quantity of gel, and also, the reaction vessel had acquired a black coating. In Example 19 of the patent, a mixture of potassium carbonate and sodium carbonate was used. The patent stated that the polymer produced had a high reduced viscosity and that a tough off-white film was formed from it. Also, no gel was present in the polymer and the reaction vessel had not become discolored.
U.S. Pat. No. 4,320,224 also describes the production of aromatic polyetherketones in the presence of an alkali metal carbonate or bicarbonate in an amount providing at least 2 gram atoms of alkali metal per mole of starting bisphenol. The patent states that the sole use of sodium carbonate and/or bicarbonate is excluded.
U.S. Pat. No. 3,941,748 describes the use of alkali metal fluoride for preparing polyarylethers. The process requires that sufficient fluoride be present so that the total fluoride available (including that from any fluoroaryl monomers) can be at least twice the number of phenol (--OH) groups. The examples show it to be, in general, a slow process.
Imai, et al., in Makromol Chem., 179, pp.2989-2991, 1978 describe the preparation of polysulfones in dipolar aprotic solvents using at least 500 mole percent of potassium fluoride based on the bisphenol. The process uses relatively low temperatures (about 100.degree. C.) to avoid polymer degradation but requires very long reaction times (48 to 70 hours).
U.S. Pat. No. 4,169,178 refers to the British counterpart of U.S. Pat. No. 3,941,748, i.e., British Pat. No. 1,348,630. The patent states that the amount of alkali metal carbonate required may be reduced in the preparation of aromatic polyethers by employing fluorophenols or difluorobenzenoid compounds as part or all of the halogen-containing reactants. The patent states that the process gives faster reactions and higher molecular weights and less colored polymers than a process using potassium fluoride in place of potassium carbonate.
German Patent Application No. 3,342,433 describes a process for the preparation of aromatic polyethers which uses a mixture of (a) a lithium and/or an alkaline earth metal carbonate and (b) a sodium, potassium, rubidium and/or cesium carbonate. The patent application states that it was totally unexpected to discover that high molecular weight polymers can be prepared via the nucleophilic polycondensation if one uses the combination of the essentially nonreactive carbonates selected from the group of lithium or alkaline earth metal carbonates, with small amounts, that are per se insufficient to perform a successful polymerization of a carbonate selected from the group of sodium, potassium, rubidium or cesium carbonates.
European Patent Application No. 182,648 discloses a process for the preparation of an aromatic polymer which comprises (a) effecting the condensation of at least one halophenol; or (b) effecting the condensation of a mixture of at least one bisphenol with at least one dihalobenzenoid compound; or (c) effecting the condensation of (i) at least one halophenol and (ii) a mixture of at least one bisphenol with at least one dihalobenzenoid compound in the presence of at least a base and at least one copper compound wherein the base is in stoichiometric excess relative to the phenolic groups in (a), (b), or (c), at least one of the compounds in (a), (b), or (c) being a compound containing a ketone group, and in the halophenol or the dihalobenzenoid compound the, or each, halogen atom being activated by an inert electron-withdrawing group in at least one of the positions ortho- or para- to the, or each, halogen atom. The patent application states that polymers of increased molecular weight, as indicated by inherent viscosity, may be obtained from chlorine- or bromine-containing monomers or a polymer of the same molecular weight or may be obtained using a shorter polymerization time. Alkali metal hydroxides, carbonates or bicarbonates are cited as useful bases.
U.S. Pat. No. 4,638,044 describes the use of sodium carbonate or bicarbonate and an alkali metal halide selected from potassium, rubidium, or cesium fluoride or chloride or combinations thereof. This process still makes use of relatively high amounts of fluoride salts which are corrosive; moreover, the rates of polymerization are relatively low.
Johnson et al., Journal of Polymer Science, A-1, vol. 5, 1967, pp. 2375-2398, compared the reactivities of various activated aromatic dihalides with an alkali metal salt of bisphenol-A in a dimethylsulfoxide solvent and concluded that aromatic fluorides are much more reactive than aromatic chlorides having the same structure and produce polyethers having a higher degree of polymerization. From the viewpoint of reactivity, fluorides are preferred. In fact fluorides may be needed to provide a high molecular weight aromatic polyether, particularly where the aromatic halo compound does not contain a sufficiently highly electron withdrawing group in a para- or ortho-position relative to the halogen atoms and the halogen atoms, therefore, are not sufficiently activated. From an economic point of view, however, chloride compounds are more advantageous because of their low cost as compared with the corresponding aromatic fluoride compound.
Reactivity of the alkali metal salt of the aromatic hydroxy compound employed as the nucleophilic monomer is also significant. Commercially, sodium and/or potassium salts are usually used. Although sodium salts are advantageous from an economic point of view, potassium salts are often chosen because the nucleophilic properties of the phenoxide anion are excellent. In a particular case where an aromatic halo compound does not contain a highly electron withdrawing group in a para- or ortho-position relative to the halogen atoms, the halogen atoms are not sufficiently activated and, because of its low reactivity such aromatic chloro compound, a high molecular weight aromatic polyether cannot be obtained unless a potassium salt is used.
Nucleophilic aromatic substitution methods for preparing polyarylene polyethers, however, involve using dipolar aprotic solvents having high boiling points, such as dimethylformamide, N-methyl pyrolidirone, dimethyl sulfoxide and diphenyl sulfone. Thus, disadvantageously, it was necessary to use additional steps and time to isolate and purify the resulting polymers after completion of the reaction. Because of the necessity for removing by-produced salts and because of the problem regarding recovery of dipolar aprotic solvents having high boiling points, conventional prior methods have certain deficiencies and disadvantages, such as poor productivity and high costs.
Thus, there exists in the prior art a need for a manufacturing process for producing polyether resins which does not use dipolar aprotic solvents having high boiling points to produce the resin. A process for preparation of high molecular weight poly(aryl ether) polymers without need of polar aprotic solvents, expensive fluoro monomers, and/or potassium salts of phenols would be more particularly advantageous.
Accordingly, an object of the invention is to eliminate or reduce the aforementioned and other disadvantages and deficiencies of the prior art processes.